There is widely known a thermographic method for analyzing the composition of a metal, according to which the impurities content in the metal is determined with reference to temperature arrests on the cooling curve of a sample of molten metal. This method makes it possible to check the carbon equivalent in molten iron with reference to the crystallization onset temperature (the liquidus temperature).
Known in the art is a digital device for automatically checking the carbon content in a molten metal with reference to the liquidus temperature (cf. U.K. Pat. No. 1,477,564). This device is applicable for determining and displaying in a digital form the carbon equivalent in molten iron with reference to the liquidus temperature, which is found as follows: EQU C.sub.E =F(T.sub.1), (1)
where
C.sub.E is the carbon equivalent; PA1 T.sub.1 is the liquidus temperature; and PA1 F is an operator defining a relation between the above values.
The device under review comprises a converter, for converting the actual temperature of the metal to a digital pulse code, which is fed at its input with a signal carrying information on the actual temperature of the metal and whose code pulse outputs, corresponding to positive and negative increments of temperature, are connected to inputs of a synchronization unit intended for time distribution of code and clock pulses. The device further comprises a clock pulse generator whose output is connected to the synchronization unit. The synchronized clock pulse output of the synchronization unit is connected to the count input of a time interval counter; the synchronized code pulse outputs of the synchronization unit are connected to add and subtract inputs of a reversible counter and a threshold counter. The threshold counter is constructed so that after the arrival of a number of pulses, corresponding to a certain value .+-..epsilon., at any of its inputs, there is formed a pulse at one of its overflow outputs. The value .epsilon..sub.o is the threshold of non-sensitivity to the temperature changes in the metal during crystallization. The overflow outputs of the threshold counter are connected to the set inputs of the time interval counter which is a non-reversible pulse counter, and is constructed so that a pulse is formed at its overflow output only on condition that a time interval between its successive settings is in excess of a predetermined threshold .tau..sub.o. The overflow output of the time interval counter is connected to the control input of a register having an information input connected to the digit outputs of the reversible counter. The register is connected through its output to a functional code converter, which converts, in accordance with the operator F, a parallel code applied to its information input from the reversible counter. The output of the functional code converter is connected to a digital display unit.
The device operates as follows. While a sample of a metal is cooling down, code pulses from the converter for converting the actual temperature of a metal to a digital pulse code, are applied through the synchronization unit to the inputs of the threshold counter and to the add and subtract inputs of the reversible counter which simultaneously generates the parallel code corresponding to the actual temperature of the metal. Each time when the temperature increment equals .+-..epsilon..sub.o, a signal is formed at an overflow output of the threshold counter. These signals arrive at the reset inputs of the time interval counter. The sychronized clock pulses are applied to the count input of the time interval counter. After each setting of the time interval counter, the counter starts time measurement, i.e. counting synchronized clock pulses. After a certain period of time .tau..sub.o has elapsed since the last setting of the time interval counter, there is formed a pulse at its overflow output. This pulse is formed only on condition that during said period of time .tau..sub.o the next pulse is not applied to the reset inputs of the time interval counter. Arriving at the control input of the register, the pulse from the overflow output of the time interval counter delivers the content of the reversible counter to the register, the content being the code corresponding to the liquidus temperature T.sub.1 of the metal. With the aid of the functional code converter, the liquidus temperature code is converted to a code corresponding to the carbon equivalent. The digital display unit displays the result in a digital form.
Thus, the above device automatically checks the carbon equivalent in a molten iron in compliance with the relationship (I).
More accurate results can be obtained if said value is determined by the difference between the liquidus temperature T.sub.1 and the solidus temperature T.sub.s. However, the known device does not provide for automatic checking of the temperature T.sub.s during the cooling of a sample of molten iron, and, therefore, does not ensure the required accuracy in determining the carbon equivalent.